1. Field of the Invention
The present invention relates to a method and apparatus for developing digital film, and specifically, to a method and apparatus for developing film by applying heat to the film.
2. Description of Related Art
In conventional digital film processing apparatuses, the film is first made sensitive to light by electrostatically charging the film. A latent image is then formed on the film by exposing the film to light from a modulated laser or similar device. The exposed film is developed by applying heat to the film.
In a first conventional film processing apparatus, a heated metal plate is provided for heating the film. The film is manually applied directly to the surface of the heated plate. The operator then manually counts a period of time, after which the film is removed from the surface of the plate. Since this arrangement requires extensive manual activity, productivity is low and film developing costs are high.
In a second conventional film processing apparatus, heating is accomplished by providing at least one heated roller between input and exit pinch rollers. The pinch rollers serve to feed the film past the heated roller while maintaining tension on the film to assure good contact with the heated roller. The film is heated by conduction through contact with the heated roller.
However, with the second arrangement, several problems arise. First, the leading and trailing edges of the film may be incompletely or poorly developed. This occurs because the leading and trailing edges are not under tension when they pass over the heated roller. As a result, sufficient contact between these edges of the film and the heated roller is not achieved.
In addition, the side edges of the film may also be poorly or incompletely developed. This is because the ends of the heated roller, which are mechanically coupled to other portions of the processing apparatus (e.g. the bearings, frame, etc.), act as heat sinks. Consequently, the temperature at the ends of the heated roller may be insufficient to properly develop the latent image at the side edges of the film. While the heated roller may be lengthened in order to provide a more uniform temperature distribution along that portion of the heated roller in contact with the film, this has the undesirable consequences of increasing both manufacturing costs and the size of the footprint of the film processing apparatus.
Moreover, during the film heating process, emulsion of the film softens and must be cooled prior to being mechanically contacted. Unless an external cooling device is provided for cooling the film prior to contact with the exit pinch rollers, the exit pinch rollers must be positioned sufficiently far down stream of the heated roller in order to permit the film to be cooled by natural convection. As a consequence, film is wasted on the leading and trailing edges.
Further, heat-developing film generally includes a polyester base which may permanently deform when heated under tension. In addition, if the film is not sufficiently cooled prior to entering the exit roller nip, further cooling occurring while the film is constrained in the nip can lead to the formation of ripples or other undesirable deformations of the film.
For the foregoing reasons, there exists a need for a film processor which can develop heat-developing film with high productivity and at lower cost. There also exists a need for a film processor which can develop the film without leading, trailing, or side edge deletion. In addition, there exists a need for a film processor that can develop heat-developing film while maintaining dimensional stability of the film.